Because the current inhalation exposure standards for lead sulfide are 3- fold greater than for lead sulfide, these chemicals were nominated by NIOSH for testing. A workshop of scientific experts concluded that initial studies should address the comparative bioavailability of different types of lead ores and pure lead salts to determine the scope of any additional studies on lead toxicity that might be conducted by the inhalation route. A contract research project was initiated to compare the toxicity and bioavailability of lead oxide, lead sulfide, lead acetate, and a sample of lead ore concentrate from Alaska. The chemicals will be fed to rats for 30 days and their blood lead levels monitored weekly. At study termination blood and bone lead, and urinary aminolevulinic acid will be measured. In addition, in-house research studies will be conducted to evaluate the biochemical toxicity of the different lead compounds in the blood and brain.